NIPT: Non-invasive prenatal testing
17th June 2018
NIPT and prenatal screening
NIPT stands for non-invasive prenatal testing. Dr Imogen Staveley (GP), sets out what you need to know.
Firstly, ‘NIPT’ is a generic term for multiple genetic screening tests that are available. Different companies organize different tests, sometimes marketed as branded versions.
The most common genetic disorder is Down’s syndrome. Babies born with Down’s syndrome have learning disabilities and physical attributes characteristic of the condition. As a result, they’re more likely to suffer physical complications like heart problems. Consequently, this reduces life expectancy.
Tests can detect Down’s syndrome prenatally. The NHS offers prenatal screening at 10 and 14 weeks of pregnancy, for Down’s syndrome as well as Edwards’ and Patau’s, known as ‘combined screening. Combined screening is via ultrasound, and blood test. It doesn’t pose a risk to the baby.
Combined screening tests for the probability of the risk of certain genetic disorders in the unborn baby. It’s not diagnostic. You’ll be offered NIPT if combined screening indicates your baby is at high risk of Down’s.
What is NIPT?
NIPT is a relatively new on the NHS. It’s called ‘non-invasive’ because it involves drawing blood from the mother, therefore doesn’t pose risk to the baby. It’s a screening test, so it’s not diagnostic. However, the likelihood of a false positive, or negative with NIPT is lower than with the initial combined test.
In short, NIPT can tell you, with greater accuracy, how likely it is that the unborn baby is at risk of certain genetic disorders. It cannot tell you with certainty.
What happens after NIPT?
If your results indicate a low risk, you likely won’t be offered further tests. The NHS will offer additional, diagnostic testing if you’re determined to be higher risk.
Further tests are diagnostic, so they tell you for certain. These are called ‘amniocentesis’ or ‘chorionic villus sampling’. Read more about these on the NHS website: http://bit.ly/amnioNHS and http://bit.ly/CVSNHS.
These tests pose a risk to the unborn baby, in that 0.5 to 1 in every 100 tests results in a miscarriage. It’s entirely up to you whether you have these tests. Because of this, the NHS recommends weighing up the risk of miscarriage against how important the results are to you.
Why do women choose to have tests?
Women choose screening further diagnostic tests for all sorts of reasons. Some parents want to know if their baby will be born with Down’s (or Edwards’ or Patau’s) syndrome so they can better prepare. Others want to know earlier so they can terminate the pregnancy, based on results.
It’s your right to choose, so it’s important you understand your choices.
Ultimately, this is a complex decision with ethical and emotional implications. Because no two women are the same, this is an individual decision. Discussing it with your partner, friends and trusted circle may help. I hope this blog helps provide information and additional resources.
Should you have NIPT on the NHS, or privately?
First of all, cost is a factor: NIPT can cost anywhere from £350 to ~£600 privately. Whether this is ‘worth it’ depends entirely on why you’re getting tested. Additionally, think about what you’d do, if you found out the baby was high-risk or positive.
Private screening can take place at 9 weeks versus 10. Depending on the woman’s point of view and reasons for testing, early testing can be beneficial. If you know earlier, you can have the option of diagnostic testing earlier. If you choose to terminate the pregnancy based on positive results, it would be better to do so earlier.
It’s also quicker to go privately in the sense that you can avoid taking the ‘combined’ screening test first, then having the NIPT (and then choosing to go for a diagnostic test should you want to). Keep in mind that NIPT is only available on the NHS to women who are classified as ‘high-risk’ via combined screening. This can sometimes mean women with a false ‘low–risk’ result could be carrying a baby with Down’s syndrome. Depending on your views and financial position, you may want to bypass the combined test and be screened privately.
As mentioned before, NIPT is a generic term referring to lots of tests that may have branded names. When you have NIPT done privately, you can’t buy the test directly from the company performing the analysis. You go through a private clinic. Because of this, navigating the range of available tests can become a minefield.
Some NHS hospitals have private wings offering NIPT, e.g. the Kensington Wing, of Chelsea and Westminster Hospital or Imperial Private Healthcare based at Queen Charlotte’s wing of the Hammersmith Hospital.
Understanding the accuracy of screening
It’s important to understand the accuracy of combined screening and NIPT. Results can sometimes return ‘false positives’. The UK’s Screening Committee sets standards for how many false positives are returned per 100 tests.
A false positive is when test results indicate that the baby has a high likelihood of having Down’s syndrome, when they in fact do not. For the combined screening option on the NHS, the National Screening Committee sets the acceptable rate at 3 false positives per 100 tests. This means every 3 in 100 tests will return an inaccurate result.
In contrast, for NIPT, the acceptable false positive rate is 0.1%, which is around 1 in every 1,000 tests.
Understanding the detection rate
The detection rate is the number of babies who truly have Down’s syndrome that are picked up by a test. This has to be over 75% for combined screening. By contrast, the NIPT’s detection rate is >98%.
So, with NIPT you’re more likely to get accurate results. Although the result isn’t diagnostic, it’s closer to being so as compared to combined screening results.
The below checklist is handy when navigating NIPT privately.
- Does the clinic offer a scan first to check dates?
- Do trained nurses, midwives, doctors or technicians perform the scan and explain dates?
- Does the clinic have links with local NHS or private hospitals?
- How much is the test? What does that include (some add on costs for different options within the test)?
- Which lab does the clinic use? Do large-scale clinical trials validate the test? Do reputable medical journals, like the Lancet, publish research into the test?
- How frequently is the test invalid? Do you ever need to repeat it? What does repeating the test cost?
- How does the clinic communicate the result? Do they offer any post-result support or counseling?
- What days and times does the clinic offer the testing?
Because this is a difficult decision, I recommend you discuss with your midwife and/or doctor for further support.
Additional info and resources
These resources help you understand Down’s syndrome:
- Down’s syndrome information – Patient Info
- Down’s syndrome Association UK
- A World Without Down’s syndrome – BBC Documentary
Here’s a resource to help you, as a mother (or couple), decide what to do should you find your tests show high risk for Down’s syndrome: http://www.arc-uk.org/for-parents/decision-making
This resource explains prenatal screening via the NHS: https://www.nhs.uk/conditions/pregnancy-and-baby/screening-tests-abnormality-pregnant